Various types of chip LEDs have been developed. For example, the following four types of chip LEDs are generally known. A chip LED of type I is formed by molding a fiberglass-reinforced epoxy resin substrate having a metallic layer. A chip LED of type II is formed with the use of a lead frame by transfer-molding the epoxy resin. A chip LED of type III is formed by insert-molding a case in a lead frame in advance and by filling the case with the epoxy resin after mounting an LED chip. A chip LED of type IV is formed by forming a case in a fiberglass-reinforced epoxy resin substrate and filling the case with the epoxy resin like type III. In addition to these types of chip LEDs, as disclosed in the Japanese Publication for Unexamined Patent Applications, No. 107283/1980 and No. 283883/1989, there are LED lamps which are produced by forming a wiring pattern in a three dimensional manner on an injection-molded resin, without using a lead frame.
As for the chip LED of type I, since the difference in the linear expansion coefficient between the fiberglass-reinforced epoxy resin substrate (7 to 1.times.10.sup.-6 /.degree.C.) and the epoxy resin (4 to 6.times.10.sup.-5 /.degree.C.) is great, they are likely separated when heat is applied, for example, in soldering. In addition, the fiberglass-reinforced epoxy resin substrate is flat and the chip LED of this type does not have a reflecting case structure, resulting in an LED lamp with poor luminous intensity.
As for the chip LEDs of type III and type IV, since these chip LEDs have reflecting cases, the light emitted by their LED chips is effectively directed in the upper direction. However, they have a drawback in terms of adhesion of the lead frame and the case or adhesion of the fiberglass-reinforced epoxy resin substrate and the case, and are not resistant to high temperatures in soldering like type I. Furthermore, with respect to types III and IV, insert-molding the case in the lead frame and bonding of the case to the substrate respectively increase the manufacturing costs.
As for the chip LED of type II, since it does not have a reflecting case, the light emitted by the LED chip is scattered in the forward direction and therefore the light is not efficiently directed in the upper direction.
On the other hand, the chip LEDs disclosed in the Japanese Publication for Unexamined Patent Applications, No. 107283/1980 and No. 283883/1989, have an insulating block body. Each block body has a reflecting case (a cavity) in the form of a recess at the center in its top surface. The sides of the cavity slope. The cavity, top surface, side surfaces and part of the bottom surface of the block body are covered with a pair of electrode patterns (plated layer). In such chip LEDs, the reflecting case and the electrode patterns are united. This arrangement therefore overcomes the problem, i.e., insufficient adhesion of the lead frame and reflecting case, associated with the above-mentioned chip LEDs using lead frames, and reduces the manufacturing costs
However, in the chip LEDs having the electrode patterns formed on the insulating block body by plating, when sealing the cavities in a substrate whereon a number of chip LEDs are produced, an epoxy resin is dropped into each cavity. Therefore, even if a small amount of the epoxy resin overflows from a cavity, the resin flows to the bottom of the block body through its through-hole which is necessary for chemical plating and for forming electrodes on the top and bottom surfaces of the substrate. When the epoxy resin flows to the bottom of the block body, soldering cannot be performed properly in mounting the chip LED as a product. This problem is solved by increasing the capacity of the cavity. However, the cavity with an increased capacity causes an increase in the size of the chip LED. The resulting chip LED does not meet demand for smaller and thinner chip LEDs. Therefore, the chip LED is always formed with a cavity of the minimum possible capacity. Consequently, the resin must be poured into each cavity on the substrate with precision.
To increase the light emission efficiency of the LED lamp, the sides of the cavity must slope at a small angle between 30.degree. and 70.degree.. However, if the cavity becomes shallower, the epoxy resin more likely overflows. The reason for this is that the viscosity of the epoxy resin momentary decreases during heat curing and it spreads around the cavity when it comes to a level higher than the brim of the cavity.
Moreover, if the cavity is shallow, the adhesion of the epoxy resin and reflecting case becomes weaker and the epoxy resin and the reflecting case are easily separated from each other when heat is applied, for example, in soldering. Namely, when the cavity is formed in the above-mentioned shape, the light emission efficiency and the quality of the product improve. However, this causes complicated manufacturing processes and an increase in the manufacturing costs.
In the meantime, the chip LED is mounted on and electrically joined to one of the electrode patterns, and is connected to the other electrode pattern with a metallic wire.
In a chip LED of this type, since the respective electrodes are formed over the entire side surfaces of the block body and on the surface of the cavity in which the translucent resin is poured, solder may climb the side surfaces of the electrodes to the top surface of the LED in surface-mounting. As a result, the appearance of the product after mounted, and the quality of the translucent resin deteriorate. Moreover, when the electrodes are formed in the above-mentioned manner, they consume a large amount of solder, causing so-called Manhattan Phenomena (in which the chip part falls over).